Allow building without grunt installed globally
Allow building without grunt installed globally

Currently `npm install` in a fresh checkout. First it complains that it can't
find the `grunt` command, after installing that it complains about grunt not
finding the `rimraf` module.

This change adds both modules to `devDependencies`, which is sufficient for the
prepublish task to pick them up.

ensime/ensime-node,ensime/ensime-node,hedefalk/ensime-node,Jarlakxen/ensime-node,Jarlakxen/ensime-node,hedefalk/ensime-node